1. Technical Field
The invention relates to a zoom lens for use in a video camera and a television camera compatible with HD, particularly, to a rear-focusing type zoom lens configured to perform focusing by moving a lens group being disposed on an image side of a first group and an imaging apparatus having the rear-focusing type zoom lens.
2. Description of the Related Art
In the field of a zoom lens, a rear-focusing type zoom lens that performs focusing by moving a lens group being disposed on the image side of a first group is known. As compared with a system in which the first lens group is moved to perform focusing, the rear-focusing type zoom lens can reduce an effective diameter of the first lens group. Furthermore, a rear-focusing type zoom lens performs focusing by moving a light-weight lens group, and thus it is possible to perform quick focusing. For example, JP Hei. 11-101941 A and JP Hei. 11-287952 A describe rear-focusing type zoom lenses that have, in order from the object side, a positive first group, a negative second group, a positive third group, and a negative fourth group. In the lenses, the second group and the fourth group are moved during zooming, and the fourth group is moved to perform focusing.
In general, when a lens system is mounted on a camera compatible with high image quality, a predetermined back focal length is required in order to arrange an optical member such as a color separation prism. Meanwhile, a zoom lens having a wide angle and a high zoom ratio is required. However, generally, when a lens is designed to have a short focal length, it is difficult to obtain a long back focal length while maintaining a high optical performance. In the related art, if it is intended to obtain a wide-angle lens having 85 degrees or more in angle of view while ensuring a sufficiently long back focal length, field of curvature at a telephoto end deteriorates. Thus, it is difficult to achieve high zoom ratio. For example, in any of the zoom lenses described in disclosed in JP Hei. 11-101941 A and JP Hei. 11-287952 A, a good balance between a high zoom ratio and widening of angle of view cannot be achieved. The following problems are accompanied by widening of the angle of view of the rear-focusing type zoom lens. That is, a back focal length is shortened, lateral chromatic aberration and distortion are deteriorated, it is difficult to achieve a high zoom ratio because aberration fluctuation caused by zooming increases, a diameter of the first group increases, and the like. Accordingly, it has been demanded to solve these problems and to develop a zoom lens that achieves a good balance between widening of an angle of view and a high zoom ratio.